/* -*- c++ -*- */
/*
 * Copyright 2016,2018 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * GNU Radio is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3, or (at your option)
 * any later version.
 *
 * GNU Radio is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with GNU Radio; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#include <flat_fader_impl.h>
#include <gnuradio/math.h>

namespace gr {
  namespace channels {

    flat_fader_impl::flat_fader_impl(unsigned int N, float fDTs, bool LOS, float K, int seed ) :
        seed_1((int)seed),
        dist_1(-GR_M_PI, GR_M_PI),
        rv_1( seed_1, dist_1 ), // U(-pi,pi)

        seed_2((int)seed+1),
        dist_2(0, 1),
        rv_2( seed_2, dist_2 ), // U(0,1)

        d_N(N),
        d_fDTs(fDTs),
        d_theta(rv_1()),
        d_theta_los(rv_1()),
        d_step( powf(0.00125*fDTs, 1.1) ),  // max step size approximated from Table 2
        d_m(0),
        d_K(K),
        d_LOS(LOS),

        d_psi(d_N+1, 0),
        d_phi(d_N+1, 0),

        d_table(8*1024),

        scale_sin(sqrtf(1.0/d_N)),
        scale_los(sqrtf(d_K)/sqrtf(d_K+1)),
        scale_nlos(1/sqrtf(d_K+1))
    {
        // generate initial phase values
        for(int i=0; i<d_N+1; i++){
          d_psi[i] = rv_1();
          d_phi[i] = rv_1();
        }
    }

#if FASTSINCOS == 1
#define _GRFASTSIN(x)   gr::fxpt::sin(gr::fxpt::float_to_fixed(x))
#define _GRFASTCOS(x)   gr::fxpt::cos(gr::fxpt::float_to_fixed(x))
#elif FASTSINCOS == 2
#define _GRFASTSIN(x)   d_table.sin(x)
#define _GRFASTCOS(x)   d_table.cos(x)
#else
#define _GRFASTSIN(x)   sin(x)
#define _GRFASTCOS(x)   cos(x)
#endif

    void flat_fader_impl::next_samples(std::vector<gr_complex> &Hvec, int n_samples){
        Hvec.resize(n_samples);
        for(int i = 0; i < n_samples; i++){
            gr_complex H(0,0);
            for(int n=1; n<d_N+1; n++){
                float alpha_n = (2*GR_M_PI*n - GR_M_PI + d_theta)/(4*d_N);
                d_psi[n] = fmod(d_psi[n] + 2*GR_M_PI*d_fDTs*_GRFASTCOS(alpha_n), 2*GR_M_PI);
                d_phi[n] = fmod(d_phi[n] + 2*GR_M_PI*d_fDTs*_GRFASTCOS(alpha_n), 2*GR_M_PI);
                float s_i = scale_sin*_GRFASTCOS(d_psi[n]);
                float s_q = scale_sin*_GRFASTSIN(d_phi[n]);
                H += gr_complex(s_i, s_q);
                }
    
            if(d_LOS){
                d_psi[0] = fmod(d_psi[0] + 2*GR_M_PI*d_fDTs*_GRFASTCOS(d_theta_los), 2*GR_M_PI);
                float los_i = scale_los*_GRFASTCOS(d_psi[0]);
                float los_q = scale_los*_GRFASTSIN(d_psi[0]);
                H = H*scale_nlos + gr_complex(los_i,los_q);
                }
    
            update_theta();
            Hvec[i] = H;
        }
        
    }

    gr_complex flat_fader_impl::next_sample(){
        std::vector<gr_complex> v(1);
        next_samples(v,1);
        return v[0];
    }

    void flat_fader_impl::update_theta()
    {
        d_theta += (d_step*rv_2());
        if(d_theta > GR_M_PI){
            d_theta = GR_M_PI; d_step = -d_step;
        } else if(d_theta < -GR_M_PI){
            d_theta = -GR_M_PI; d_step = -d_step;
        }
    }

  } /* namespace channels */
} /* namespace gr */
